1. Field of the Invention
The present invention relates to a method for manufacturing the ink discharge port of an ink jet recording head that enables ink droplets to fly and adhere to a recording medium, and also, relates to an ink jet recording head provided with the ink discharge port manufactured by such method of manufacture.
2. Related Background Art
Conventionally, for the processing of the ink discharge port of the ink jet recording head, which is made adaptable to the ink jet recording method, sublimation etching, which cuts the covalent binding of carbon atom by means of photo-chemical reaction, has been in use in recent years with patterning irradiation of excimer laser or some other high-energy ultraviolet laser for the formation of a structure on resin material. It has been in practice, then, to implement a structural formation of the kind by use of such laser beam processing.
Also, as another method thereof, which is called electro-forming, non-conductive material is patterned on a conductive base plate, and subsequently, metal is developed in a thick film form by means of electrolysis plating, and then, a hole portion formed on the non-conductive material is used as the ink discharge port, or there is a method in which a thin metallic plate is mechanically punched by use of a hole-type punching die for the formation of the ink discharge port, or there is still another method in which on an IC chip having a source for generating pressure for the ink discharge port, a photosensitive negative resist, which forms the ink discharge port, is coated in a laminating process, and then, the ink discharge port is formed by means of exposure development.
On the other hand, as a method for discharging ink, it has been practiced to make the interior of the ink discharge-port holes hydrophilic to liquid ink, while giving water repellency to liquid ink on the area from the hole-edges to the circumference on the ink discharging side. In this manner, an ink liquid interface is formed on the surface of the ink discharging side by means of liquid surface tension, and with the pressure exerted on liquid ink by use of a mechanically displacing element or thermo-bubbling element, liquid ink retained in the interior of the ink jet is pushed out to enable ink droplets to fly.
In this respect, the wall face of the ink discharge port formed inside the ink discharge surface is finished to be extremely smooth by any one of the methods for processing the ink discharge port, and the wall surface is processed and formed to a state having irregularities of 0.2 micrometer or less as the standard deviation value for the surface roughness thereof.
With the wall face of the ink discharge port thus finished, the flow resistance thereof becomes less, which is preferable in terms of the flowability of ink. However, it has been found recently that from the viewpoint of the ink discharging characteristics of the ink jet recording head, there exists the following drawback:
1. In order to make the recording speed faster, it is necessary to increase the ink discharge frequency. However, there is a limit to the ink discharge frequency due to the fact that unless the meniscus vibration, which,is the attenuating vibration of ink liquid surface tension by the surface tension created subsequent to the discharge of an ink liquid droplet, is settled, the next ink liquid droplet cannot be discharged stably. Thus, the ink discharge frequency is determined by the time required for the settling of the meniscus vibration. Ere, if the resistance to ink flow is small, the settling time of the meniscus vibration is made longer eventually.
2. The meniscus vibration that follows ink discharge is generated by the ink supply from the ink liquid chamber, which functions as an ink buffer, to compensate for the volume of ink that has been discharged. Here, if the flow resistance encountered by the ink is small, overshooting takes place by the inertia of fluid movement at the time of such supply, thus making the amount of extrusion of the ink liquid surface greater on the ink discharge surface, that is, the amplitude of meniscus vibration itself is caused to become greater eventually.
3. If the contact area of ink is small with respect to the ink that resides on the wall face of the ink discharge port, ink tends to be peeled off partially from the wall face of the ink discharge port when discharged, and outside air is caught inevitably inside the ink nozzle. As a result, outside air enters the interior of the head as bubble in a gaseous state, which tends to push out liquid ink retained inside the ink jet. Such mixed bubble partially absorbs the pressure exerted by the mechanically displacing element or thermo-bubbling element, hence making it impossible to obtain sufficient ink discharge power eventually.
4. If the contact area of ink is small with respect to the ink that resides on the wall face of the ink discharge port, the attractive force exerted by the hydrophilic contact between ink and the wall face of the ink discharge port is made smaller, and the supplying force of ink from the ink chamber serving as the ink buffer, which compensates for the volume of ink that has been discharged, is made weaker, thus lowering the supplying speed of the ink.
Now, if the flow resistance of the wall face of ink discharge port is small, such obstacles as described above are encountered when it is attempted to make the recording speed higher by increasing the ink discharge frequency. Also, such problems as described above are encountered as those related to ink discharges.